Propeller.



E. D. SPEAR.

' PROPELLER.

Patented Jan. 12, 1909.

V Il!! M BNITED 'UATFQNT @ldlltlli EDMUND D. SPEAK, OF BOSTON,MASSACHUSETTS.

PROPELLER.

AppIication led December 19, l.

To all whom tt 'may concern.'

Be it known that T. llnirifno D. Srnrxn, of Boston, in the county ofSuffolk and State of l/lassachusetts, have invented a new and usefulImprovement in Propellers, of which the following is a specification.

In designing propeller blades so far as l have been able to learn,Jthere has been a great deal of experiment with comparatively littlesatisfactory result. lhat shall be the shape of the blade in any givencase, while it may have been figured out by the rules of physics and byvarious formulae, has never 'been decided without some qualificationwhich has prevented the propeller from being the success, from amechanical standpoint, which has been intended.

ln studying the subject of wave motion as occurs in any fluid mediumsuch as water or an allied substance, the air, l have noted. the factthat when waves are set in motion or cu-rrents formed,- they have beenproduced the most quickly and with the least loss of power' where theopposing or actuating surface which causes this motion is curved withthe curve known as the conchoidal curve. As a curved surface of thisdescription. can from its nature present no focus or center forconverging` air waves or liquid waves, as of water. but distributes suchwaves or currents without so doing, z'. c., focusing them, it has seemedbest suited to my purposes in the construction of my propeller blades.lts utility may be readily shown by forming an ear trumpet in suchmanner that the passage through it shall be of this conchoida-l shape,that is, substantially the shape of the passages from the exterior tot-he interior of a conch shell, and comparing its efficiency with theefliciency of any of the ear trumpets of ordinary construction. Thereason for this, as l believe. is that there is practically no chancefor interference between the various waves which are received at theembouchure (bell mouth entrance) of such an ear trumpet and are conveyedalong therefrom to the small opening made for application to theexternal canal of the ear. ln such case aerial vibrations Within the eartrumpet may be considered as conveyed towards the smaller end withoutmeeting with or obstructing the passage of similar vibrations taking thesame course. My invention is based upon the application of this samediscovery to the construction of propellers, and it con- Specication ofLetters Patent.

Patented aan. 1a, reco.

Serial No. 86,548.

sists in a propeller provided with two or more blades, one or bothsurfaces of which blades are conchoidal.

lily invention will be understood by reference to the drawings, inwhich- Figure i is an end elevation of a propeller embodying myinvention, Fig. 2 being a side elevation thereof, and F ig. 3 a topView.

A is the hub of ordinary construction, from which project the two bladesB, B. I prefer to make the blades with a double curve as shown in Fig.3, one half of the blade projecting rearward and the other half 1projecting forward in order that the blade may be equally eflicientwhether it is working forward or backward. ln any case the peculiarityof the blade is such that its working surface being conchoidal in shapethe particles impinging upon it are forced from its surface practicallyin one given direction, that is, in a constantly increasing anddiverging direction from each other without interference, and hence withbut slight resistance other than -that due to friction against thesurface of the blade.

ln operation the leading edge and advancing surface of each blade B whenr0- tating enters new water to advance the propeller and ship to whichit is attached, but because of the curved shape of this advancingsurface and because of the absence of those foci and of eddies usuallyproduced by other curved surfaces having foci, there is no interference,that is, no tendency on the part of one wave (of water) to interfere inany way with another wave (of water). Hence the resistance in front ofthe blade is reduced to a comparatively lsmall amount while the pressurebehind the propeller is not materially reduced.

l prefer to so locate the blades about the hub that their bases will beat an angle of between 20 and 300 with its aXis. As each blade spreadspreferably from the hub to its extremity the leading edge or enteringcorner of the blade is in a plane nearly parallel with the axis ofrotation so that it cuts the new water with practically no resistance.This result is in my opinion, due entirely to the peculiar propertywhich the convex surface, in this case also conchoidal, has of behavingin the same manner as the concave, and conchoidal surface, as regardsinterference.

l have described my propeller as for use in Water, but I believe itwould bey equally eliicient in air.

I am aware that propellers have been constructed, the blades of whichhave cross sections representing reversed or inflected Y plurality ofbladeseach projecting from said hub, each of said blades having alateral cross section m the formof reversed oonchoidal curves, the saidconchoidal curves appearing in every part of the blade. i

Q. A propeller comprising a hub and a plurality of blades each of whichhas a driving'V surface in the form of a conveXed conchoidal curveextending transversely thereof.

,In testimony whereof, I hereunto set my pname this thlday of October,1901.

, EDMUND D. SPEAK.

lVit'n'esses ALFRED Slimm- Gnonon O. Gr. CoALE.

